It is often desired to separate target molecules from complex mixtures, such as body fluids. The target molecule may be any biomolecule present in such a fluid, for example protein, peptide, nucleic acid and carbohydrates. Most often this requires pre-fractionation of the sample or some kind of sample preparation. Sample preparation is conventionally performed by chromatography or electrophoresis.
For chromatography on columns the sample flow, in binding or elution mode, is in one direction, i.e. the sample is usually loaded on the top of the column and collected at the bottom of the column.
Another way of achieving sample preparation is by using pipette tips filled with separation media. In prior art pipette tips for sample preparation, the sample is drawn into the pipette tip and is allowed to react with the separation media in the tip. The sample is drawn into the same channel of the pipette tip as it is later expelled from the pipette tip when the desired contact with the separation media has occurred. Thus, the flow of sample in the pipette tip is in two opposite directions, first into the tip and then out of the tip. This has a number of drawbacks, for example the separation media will be contaminated with sample constituents already when the sample is moving into the pipette which impairs the separation of the desired target molecules when the sample is flowing out of the tip and collected. Furthermore, the separation media in the pipette tip may be clogged with sample proteins and other molecules on their way up in the tip which will make it impossible to elute any proteins of interest in the outflow from the tip.
Therefore, there is a need within the sample preparation area to provide a convenient device which avoids the above drawbacks but still provides the desired separation.